Fuzz Face Collector Voltages

[Arn C.]

Howdy All,
    I built a fuzz face circuit and I am attempting to set the collector voltages.   I set Q1 at 1.10v and I can only get as high as 2.4v at Q2.

I am using a 50K trimpot on Q1 and a 25K trimpot on Q2.

What culd be wrong?  I think I am supposed to get 1/2 the supply at Q2 collector.
I am doing the PNP version.

Thanks!
Arn C.

[Arn C.]

Can anyone help me with this?

Thanks!
Arn C.

[Jim Jones]

Hey Arn,

Check out some of the articles at Runoffgroove - I believe they have some voltages posted for a number of FF-style projects.  Ideally 1/2 your supply is what you're going for on Q2's collector - I can't remember the ideal Q1 C voltage...

Jim

[Arn C.]

Thanks Jim for the info!!!

Does anyone know what I have to do to get the voltage up on Q2?

Peace!
Arn C.

[Jason M.]

Are you using germanium transistors?
Did you test them for leakage and gain?

I use a 25k pot on Q2's collector and haven't had trouble getting the bias right, unless the transistors have too much leakage.

1/2 supply voltage on Q2's collector is a reference point. I just tweak the bias until I like the sound.

[ErikMiller]

Try bringing the Q1 collector voltage down, and you may be able to get the Q2 collector voltage up.

[Arn C.]

I tweaked the first collector voltage until Q2 collector voltage came up to 4.45 volts, Q1 now has a collector voltage of 4.1v  .  Will this work this way?



Thanks gents for the info!!!!

Arn C.

[Jim Jones]

Hey Arn,

Here's another page that may be of assistance.  http://www.geocities.com/SunsetStrip/Studio/2987/britface.html

Jim

[aron]

Are you sure you have the transistor oriented correctly?

Finally, do you have the feedback resistor in there? The one that goes from the emitter of Q2 to Q1's base?

[Arn C.]

Thanks Jim!

Aron wrote:
[/quote]Are you sure you have the transistor oriented correctly?

Yes!

Aron wrote:

Finally, do you have the feedback resistor in there? The one that goes from the emitter of Q2 to Q1's base?

Yes!

Arn C.

[RDV]

What is the measured voltage right before it goes into the trimmer pot at Q2? It should the 9v- rail.

Regards

RDV

[Arn C.]

I made the pnp fuzz face if that helps any.........
I tweaked the first collector voltage until Q2 collector voltage came up to 4.45 volts, Q1 now has a collector voltage of 4.1v . Will this work this way?   Or does Q1 need to be much lower?  I read somewhere 1.10 volts for Q1 is good.

Arn C.

[Arn C.]

Bump

[Jim Jones]

Hey Arn,

As you said, I think that Q1's collector needs to be much lower.  What value resistors are you using for both collectors?

Jim

[B Tremblay]

Did you use germanium or silicon transistors?

Check this page for some sample voltages of Fuzz Faces built with both types (toward the bottom): http://runoffgroove.com/tbmk2.html

[Arn C.]

[/url]http://www.muzique.com/schem/fuzzface.gif//I%20have%20all%20the%20same%20value%20components%20as%20in%20the%20pnp%20schematic%20at%20the%20above%20site%20except%20that%20I%20have%20a%2050k%20trimpot%20for%20Q1%20collector%20instead%20of%20resistor%20and%20a%2025k%20trimpot%20for%20the%20collector%20of%20Q2%20instead%20of%20resistor.I%20now%20have%20it%20set%20for%204.45%20volts%20on%20Q2%20collector,%20and%20Q1%20is%20reading%204.1volts%20on%20collector.%20%20If%20I%20try%20to%20lower%20Q1%20,%20Q2%20also%20lowers.At%20first%20I%20set%20Q1%20for%201.10%20volts%20and%20Q2%20read%202.4%20volts%20maximum,%20%20then%20I%20raised%20Q1%20and%20Q2%20raised%20also.Arn%20C.

[B Tremblay]

What are the other pin voltages?  And are you using germanium or silicon transistors?

[Arn C.]

Ok, here we go again.

I decided to make an NPN fuzzface and see if it comes out without the problems I have been having with the pnp ff.

Well, same problem.  With the NPN ff  I only had the first transistor(Q1) and for the second(Q2) I used a metal can silicon.   I tried to get the hfe's correct  (around 74 for the Q1 and 132 for Q2)

With 9 volts applied to the circuit  I had the same problem as before.  This time I decided to change the resistor between Q1 and Q2(9 volt line) the 330 ohm resistor on the npn ff.   I put in a resistance decade box and fiddled around until I finally got the voltages to read correctly.  4.5 on Q2 collector and 1.24 on Q1 collector.    

The extra added resistance was  430K !!!!

Q1  C=1.24 B=.088 E=0
Q2  C=4.50 B=1.22 E=.766

Do these values look okay now ?  
Will the circuit now work okay?

Thanks!
Arn C.